Optical circuit in which fabrication is easy

ABSTRACT

In a method for fabricating an optical circuit, a mirror element with a protection film formed within a die of a semiconductor is connected to a substrate at a predetermined position. The mirror element with the protection film connected to the substrate is peeled from the die of the semiconductor. The protection film is removed to expose a reflection surface of a reflection film of the mirror element.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an optical circuit and a methodfor fabricating the same.

[0003] 2. Description of the Related Art

[0004] Request for a large capacity of data transmission have beenincreased. A parallel transmission has been discussed for carrying outthe data transmissions between computer terminals, between switches andbetween large computers, in a real time and in parallel. Also, theprovision of an advanced information service to a home has beendiscussed. The spread of optical communication is desired for the sakeof such large capacity of data transmission.

[0005] For the optical communication is used an optical module composedof optical elements such as an optical fiber, a semiconductor laser(LD), a light emission diode (LED), a photo-diode (PD), an opticalswitch, an optical isolator and an optical waveguide. The applicationfield of the optical element used in such an optical module is expandedsince its property and its function are made higher. The cost-down ofnot only an individual optical element but also the optical module isrequired to provide the advanced information service to the home. Inorder to attain the cost-down, the optical module is desirablyfabricated in not a coaxial type module structure in which opticalelements are arrayed in a form of block, but a flat type optical modulestructure in which a plurality of optical elements are arrayed on a samesubstrate.

[0006]FIG. 1 shows an optical circuit of a bi-directional communicationmodule in a first conventional example. A semiconductor laser LD 102, aphoto-diode PD 103, an optical waveguide 104, a wavelength filter 105and an optical fiber 106 are mounted on a Si substrate 101. Light havingthe wavelength of 1.3 μm is emitted from the semiconductor laser LD 102as a light source to the optical waveguide 104, travels through thewavelength filter 104 and then transmitted to a reception side throughthe optical fiber 106 as a transmission path. Signal light having thewavelength of 1.5 μm is sent through the optical fiber 106, and isinputted to the optical waveguide 104. The optical path of the signallight is changed to an adjacent waveguide by the wavelength filter 105,and then inputted to the photodiode PD 103. Thus, the reception of thesignal light is carried out. In this way, a small transmission/receptionoptical module can be attained by use of the flat optical circuit.Grooves are formed on the Si substrate 101 by use of the well-knownsemiconductor processing technique and used to position the opticalwaveguide 104, the wavelength filter 105 and the optical fiber 106.

[0007] As the optical elements are contained optical elements such as asurface light emission element, a surface light reception element, anend surface light emission element and an end surface light receptionelement. In the surface light emission element and the surface lightreception element, an optical axis is oriented to a direction verticalto a substrate surface. In end surface light emission element and theend surface light reception element, an optical axis is oriented to adirection horizontal to a substrate surface. When two kinds of theoptical elements in which the directions of the optical axes areorthogonal to each other are mixed and mounted on the same substrate, itis necessary to change or convert the optical path by 90 degrees.Masataka Itoh et al., (46-th, Electronic Component & TechnologyConference, p.1) (a second conventional example) propose an optical pathchange technique. In this technique, as shown in FIG. 2, an optical pathof output light from the optical fiber 106 is changed into the directionof the photo-diode PD 103 by reflecting the output light on a slantsurface 109 formed by an anisotropic etching of the silicon substrate101. In this method, however, the substrate material is limited to thesilicon. Thus, the method cannot be applied to other substrates.

[0008] A prism for an optical path change is known from Japanese LaidOpen Patent Application (JP-A-Heisei, 7-159658) (a third conventionalexample), as shown in FIG. 3. An optical path of a light beam 107emitted from the optical waveguide 104 is changed by 90 degrees by aprism 108 or a reflection surface 109 of a reflection mirror. In thiscase, if the prism having the size of 1 mm or less is used, afabrication cost of the prism is expensive to further increase afabrication cost of the optical module.

[0009]FIG. 4 shows an installation example of an optical element whenthe optical path is not changed (a fourth conventional example). Inorder to mount the light receiving surface of a photo-diode PD 103 in adirection orthogonal to the surface of a substrate 101, it is necessaryto newly carry out position adjustment three-dimensionally. Also, it isnecessary to add another substrate 110 for supporting the photodiode PD103 and a part for fixing the substrate at the adjusted position. Thus,the fabrication cost is further increased.

[0010] Light emitted from a light emission element such as a lightemission diode and a laser diode spreads to have a certain radiationangle. Even if a waveguide or an optical fiber is closely disposed nearthe emission portion of the light emission element, there may be a casethat the whole emission light cannot be received. Such a case results inan optical loss. For the reduction in the optical loss, a small lenshaving an excellent light collection performance needs to be used.However, it is difficult to fabricate such a small lens.

[0011] In conjunction with the above-mentioned description, JapaneseLaid Open Patent Application (JP-A-Showa, 59-7916) discloses a systemfor coupling a laser diode and a single mode of optical fiber. Accordingto this reference, a curved surface is formed on one end surface or bothend surfaces of a self-collection type lens. The lens is disposedbetween the laser diode and the single mode of optical fiber.

[0012] Also, Japanese Laid Open Patent Application (JP-A-Heisei,7-159658) discloses a coupling structure between an optical waveguideand an optical element. In this reference, the optical waveguide isformed by laminating the dielectrics different from each other. Theoptical waveguide is formed on a dielectric substrate. In front of anend of the optical waveguide on the side on which the optical element isdisposed, a groove is formed on the dielectric substrate to have abottom surface parallel to a surface of the optical waveguide. A prismis disposed in a groove in which an optical axis of the opticalwaveguide is coincident with an optical axis of the disposed opticalelement. The optical element is mounted on the dielectric substrate sothat it strides over the prism and the optical waveguide. Metallic coatis formed on one surface of the prism and the bottom surface of thegroove. Moreover, a solder sheet is disposed on the surface of the metalcoat on the bottom surface of the groove, or the solder layer is formedthereon. The prism is disposed in such a manner that the surface of theprism on which the metal coat is performed faces to the surface of thesheet or the top surface of a solder layer. The dielectric substrate andthe prism are heated to thereby melt the solder. Thus, the prism iscoupled to the dielectric substrate.

[0013] A light connection integrated circuit is disclosed in JapaneseLaid Open Patent Application (JP-A-Heisei, 9-8273). In this reference,each of first and second reflective optical elements has at least threeplanes orthogonal to each other and a plane parallel to one of the threeplanes, and further has a reflection plane that is orthogonal to the twoplanes parallel to each other and disposed for the other plane at apreset angle. Each of the first and second reflective optical elementsis formed of transparent material. A flat substrate has a flat surfaceon which the first and second reflective optical elements are disposed.A first integrated circuit having a light emission device for outputtingan optical signal and a second integrated circuit having a lightreception device for receiving the optical signal are disposed on a flatsurface opposite to the flat substrate of the integrated circuitsubstrate. The first reflective optical element converts an orientationof the optical signal outputted by the light emission device of thefirst integrated circuit into an orientation parallel to the flatsurface of the flat substrate. The second reflective optical elementchanges the orientation of the optical signal parallel to the flatsurface of the flat substrate so that it is inputted to the lightreception device of the second integrated circuit.

[0014] Also, an optical path changing method is disclosed in JapanesePatent No. 2,687,859. In this reference, a micro lens is disposed on amount substrate or a sub-substrate different from the mount substrate.An outer side of the micro lens is used as a light reflection surface.Then, the optical path is converted by about 90 degrees from ahorizontal direction to a vertical direction, or reverse. The outersurface of the micro lens may be a spherical surface, or metal coatingmay be performed on the surface of the micro lens.

SUMMARY OF THE INVENTION

[0015] Therefore, an object of the present invention is to provide anoptical path change device that can be fabricated at a low cost, and amethod for fabricating the same.

[0016] Another object of the present invention is to provide an opticalelement in which the change of an optical path and the collection oflight can be carried out, and a method for fabricating the same.

[0017] Still another object of the present invention is to provide anoptical circuit using one of the above-mentioned optical elements, and amethod for fabricating the same.

[0018] Yet still another object of the present invention is to providean optical circuit that can be fabricated at a low cost, and a methodfor fabricating the same.

[0019] Another object of the present invention is also to provide anoptically flat circuit in which optical elements are easily mounted, anda method for fabricating the same.

[0020] In an aspect of the present invention, a method for fabricatingan optical circuit is attained by: (a) joining a mirror element with aprotection film formed within a die of a semiconductor to a substrate ata preset position; (b) stripping the mirror element with the protectionfilm joined to the substrate from a die of the semiconductor; and (c)removing the protection film so as to expose a reflection surface of areflection film of the mirror element.

[0021] The mirror element with the protection film may be installed to atip of at least one cantilever of the substrate. At this time, in themethod, an expending and contracting member for moving the tip upwardlyand downwardly may be installed below the mirror element or below thetip. The expending and contracting member is desired to be one of apiezoelectric element, an electric distortion actuator, a magneticdistortion actuator, and a phase transition material.

[0022] Also, the (b) stripping step may comprise the step of thinning athickness of the protection film in a periphery of the mirror element,and the (c) removing step may comprise the step of removing theprotection film by a wet etching.

[0023] Also, the (a) joining step may be attained by: (d) forming theprotection film so as to cover an inner surface of a concavecorresponding to the die of the semiconductor; and (e) forming areflection film of the mirror element so as to at least cover theprotection film in the concave. In this case, the (e) forming step maycomprise the step of forming the reflection film by use of anelectrolytic plating method.

[0024] Here, the reflection film is desired to be one of: a gold film; alamination film of rhodium film-nickel film-gold film; a lamination filmof platinum film-nickel film-gold film; a lamination film of palladiumfilm-nickel film-gold film; a lamination film of gold-nickel film-goldfilm; a lamination film of nickel-boron alloy film-nickel film-goldfilm; a lamination film of nickel film-gold film; a lamination film ofchrome film-nickel film-gold film; a photosensitive polyimide film; alamination film of gold film-(Ni—P) film/Ni film-P film-Au film; and alamination film of Au film-Pt film-Au film.

[0025] Also, it is desirable to fill a remaining concave after theformation of the reflection film with a preset material. The presetmaterial is a resin composition containing an active energy linepolymerization initiator and an active energy line reaction resin.

[0026] Also, the mirror element has a join auxiliary film in a directionof the reflection surface, and the (a) joining step may be attained by:joining the join auxiliary film to the substrate; and joining the mirrorelement to the preset position of the substrate after said strip.

[0027] Also, the reflection surface of the mirror element may have aflat surface or a concave surface.

[0028] From another viewpoint of the present invention, a method forfabricating a mirror element is attained by: (a) joining a mirrorelement with a protection film formed within a die of a semiconductor toa substrate at a preset position; (b) stripping the mirror element withthe protection film joined to the substrate from a die of thesemiconductor; and (c) forming a reflection film of the mirror elementon the protection film.

[0029] At this time, the mirror element with the protection film may beinstalled to a tip of at least one cantilever of the substrate. Also,the method may further comprise the step of installing an expending andcontracting member for moving the tip upwardly and downwardly below themirror element or below the tip. In this case, the expending andcontracting member is desired to be one of a piezoelectric element, anelectric distortion actuator, a magnetic distortion actuator, and aphase transition material.

[0030] Also, the (b) stripping step comprises the step of thinning athickness of the protection film in a periphery of the mirror element.

[0031] Also, the (a) joining step may be attained by: (d) forming aprotection film so as to cover an inner surface of a concavecorresponding to the die of the semiconductor; and (e) forming themirror element so as to at least cover the protection film in theconcave.

[0032] Also, the (e) forming step may comprise the step of filling aremaining concave after the formation of the mirror element with apreset material. In this case, the preset material is desired to be aresin composition containing an active energy line polymerizationinitiator and an active energy line reaction resin.

[0033] A reflection surface of the mirror element may have a flatsurface or a concave surface.

[0034] From still another viewpoint of the present invention, a methodfor fabricating a mirror element is attained by: (a) forming aprotection film so as to cover an inner surface of a die formed in asemiconductor; (b) forming a mirror element film so as to at least coverthe protection film in the inner surface of the die; and (c) strippingfrom the semiconductor substrate the mirror element film together withthe protection film.

[0035] The method may comprise the step of: (d) removing the protectionfilm from the mirror element so that the mirror element film functionsas a reflection film, and (e) forming a reflection film on theprotection film on the protection film mirror element film.

[0036] Also, the reflection film is desired to be one of a laminationfilm of chrome film-gold film, a lamination film of a chromefilm-aluminum film, a lamination film of chrome film-silver film, alamination film of chrome film-copper film, a lamination film of chromefilm-palladium film, a lamination film of chrome film-titanium film, anda lamination film of chrome film-nickel film.

[0037] Also, the (a) forming step may be attained by: (f) forming theprotection film so as to cover the inner surface of the die formed inthe semiconductor; and (g) forming the mirror element film so as to atleast cover the protection film in the inner surface of the die. Themirror element film is desired to be formed by use of an electrolyticplating method. The mirror element film is desired to be one of: a goldfilm; a lamination film of rhodium film-nickel film-gold film; alamination film of platinum film-nickel film-gold film; a laminationfilm of palladium film-nickel film-gold film; a lamination film ofgold-nickel film-gold film; a lamination film of nickel-boron alloyfilm-nickel film-gold film; a lamination film of nickel film-gold film;a lamination film of chrome film-nickel film-gold film; a photosensitivepolyimide film; a lamination film of gold film-(Ni—P) film/Ni film-Pfilm-Au film; and a lamination film of Au film-Pt film-Au film.

[0038] Also, a remaining concave after the formation of the mirrorelement film may be filled with a preset material. The preset materialis desirable to be one of a resin composition containing an activeenergy line polymerization initiator and an active energy line reactionresin. Also, the active energy line reaction resin is one of phenolnovolak type epoxy resin, cresol/volak type epoxy resin, glycylaminetype epoxy resin and biphenyl type epoxy resin. Also, the active energyline reaction resin is desired to be substance in whichunsaturated-base-acid, such as acrylic acid, methacrylic acid, crotonicacid, maleic acid, maleic acid monomethyl, maleic acid monopropyl,maleic acid monobutyl, sorbic acid and the like, reacts with epoxy resinhaving fluorene skeleton, or epoxy resin portion of bromide of epoxyresin having fluorene skeleton, and it is made into ester. Also, theactive energy line polymerization initiator is one kind or two kinds ormore among a benzophenone class, a benzildi-methylkethal class and acompound of a thio-xanthone system.

[0039] Also, the (a) forming step may comprise the step of etching asilicon substrate and forming a concave corresponding to the die. Inthis case, the inner surface of the concave is one of a (100) surfaceand a (111) surface. Also, the concave is one of a pyramid type and atriangular pole type in which both ends are cut down.

[0040] Also, the (c) stripping step may comprise the step of thinningthe protection film in a periphery of the mirror element film.

[0041] Also, the (c) stripping step may comprise the step of strippingthe mirror element film from the die of the semiconductor after themirror element film is joined to the substrate. In this case, the mirrorelement film is desired to have a join film portion used to join to thesubstrate in a direction orthogonal to an optical axis at a time of ausage.

BRIEF DESCRIPTION OF THE DRAWINGS

[0042]FIG. 1 is a plan view showing a first conventional example of anoptical circuit;

[0043]FIG. 2 is a front view showing a second conventional example ofthe optical circuit;

[0044]FIG. 3 is a front view showing a third conventional example of theoptical circuit;

[0045]FIG. 4 is a front view showing a fourth conventional example ofthe optical circuit;

[0046]FIG. 5 is a partial sectional view showing a structure of anoptical circuit according to a first embodiment of the presentinvention;

[0047]FIGS. 6A to 6H are sectional views showing a first method forforming a mirror element used in the first embodiment;

[0048]FIG. 7 is a plan view showing a mirror on the way of fabricationof the mirror element;

[0049]FIG. 8A is a plan view showing a substrate on which the mirrorelement should be mounted in the first embodiment of the presentinvention;

[0050]FIG. 8B is a plan view showing the substrate after the mirrorelement is mounted;

[0051]FIG. 9A is a plan view showing the mirror element;

[0052]FIG. 9B is a front view showing the mirror element;

[0053]FIG. 10 is a sectional view showing a substrate on which themirror element and an optical fiber are mounted;

[0054]FIGS. 11A to 11H are sectional views showing a second method forforming a mirror element;

[0055]FIG. 12 is a plan view showing a concave portion for the mirrorelement formed by the second method;

[0056]FIGS. 13A to 13D are perspective views showing a process forassembling an optical circuit;

[0057]FIG. 14 is a plan view showing a mirror element formed by a thirdmethod;

[0058]FIG. 15 is a sectional view showing a mirror element formed by thethird method;

[0059]FIG. 16 is a partial sectional view showing an optical circuit onwhich the mirror element formed by the third method is mounted;

[0060]FIG. 17 is a plan view showing a die used when the mirror elementis formed by a fourth method;

[0061]FIG. 18 is a sectional view showing the mirror element formed bythe fourth method by use of the die shown in FIG. 17;

[0062]FIG. 19A is a plan view showing a substrate on which the mirrorelement should be mounted in a second embodiment of the presentinvention;

[0063]FIG. 19B is a plan view showing the substrate after a mirrorelement is mounted;

[0064]FIG. 20 is a plan view showing an optical circuit according to athird embodiment of the present invention;

[0065]FIG. 21 is a front partial sectional view showing the opticalcircuit according to the third embodiment of the present invention;

[0066]FIG. 22 is a plan view showing an optical circuit according to afourth embodiment of the present invention;

[0067]FIGS. 23A and 23B are sectional views showing an operation of anoptical circuit according to the fourth embodiment of the presentinvention;

[0068]FIG. 24 is a sectional view showing the mirror element formed bythe second method in an experiment example 1;

[0069]FIG. 25 is a plan view showing a resist pattern used in theexperiment example 1;

[0070]FIG. 26 is a perspective view showing a die used in the experimentexample 1;

[0071]FIG. 27 is a perspective view showing a state that the mirrorelement formed by use of the die shown in FIG. 26 is mounted on asubstrate;

[0072]FIG. 28 is a front view showing a partial section of the opticalcircuit formed by use of the substrate shown in FIG. 27;

[0073]FIGS. 29A to 29E are front sectional views showing a method forfabricating an optical circuit according to a fifth embodiment of thepresent invention;

[0074]FIGS. 30A and 30B are front views showing states of the mirrorelements after fabrication, respectively; and

[0075]FIGS. 31A and 31B are front views showing states of the mirrorelements after fabrication, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0076] An optical circuit according to the present invention will bedescribed below in detail with reference to the attached drawings.

[0077]FIG. 5 is a sectional view showing a structure of the opticalcircuit according to the first embodiment of the present invention.Referring to FIG. 5, a mirror element 1, an optical guide device 3 and alight emission/reception element 4 are mounted on an optical circuitsubstrate 2. The optical guide device 3 is an optical waveguide or anoptical fiber, for example. The light emission/reception element 4 is aphoto-diode or a surface light emission type laser element, for example.

[0078] A reflection surface of the mirror element 1 has the angle ofabout 45 degrees with respect to an optical axis of a light source. Thereflection surface of the mirror element 1 is made of a metal film. Theconnection between the mirror element 1 and the optical circuitsubstrate 2 is made of a metal film or resin. A light beam outputtedfrom the optical guide device 3 is reflected on the mirror element 1 andguided to the light reception element 4. A light beam outputted from thelight emission element 4 such as a surface light emission type laser isreflected on the mirror element 1 and inputted to the optical guidedevice 3.

[0079]FIGS. 6A to 6H show a first fabricating method for the mirrorelement 1 used in the optical circuit according to the first embodimentof the present invention. This mirror element 1 has the shape that bothends on one ridgeline of a pole portion of a triangular-prism shape arecut down toward an opposite side.

[0080] A die is used to fabricate the mirror element 1. A metal film isformed within the die such that a reflection surface is formed. Themirror element 1 is coupled to the optical circuit substrate 2 on apredetermined position. The minute mirror element 1 is not treated as asingle body. The die in which the mirror element 1 is formed is treated,and the mirror element 1 is coupled to the optical circuit substrate 2.Thus, the mirror element 1 can be easily mounted on the optical circuitsubstrate 2 at a high accuracy and at a cheaper cost.

[0081] The die used to fabricate the mirror element 1 is referred to asa silicon etch pit. As shown in FIG. 6A, thermal oxide films 6 areformed on both surfaces of a silicon wafer 5 having the crystalorientation (100) to have the thickness of 1 μm. The silicon wafer 5 hasthe diameter of 6 inches and the thickness of 1 μm. Subsequently, asshown in FIG. 6B, a photo-resist layer 7 is coated on the thermal oxidefilm 6 on one side to have the thickness of 5 μm. After the photo-resistlayer 7 is exposed by use of a desired mask, the silicon wafer 5 isdeveloped and rinsed. Thus, the photo-resist layer 7 is patterned, and afirst opening 8 is formed. The first opening 8 has the size of thelongitudinal length of 70 μm×the lateral length of 100 μm.

[0082] Next, as shown in FIG. 6C, the silicon wafer 5 with the firstopening 8 is immersed in buffered hydrofluoric acid so that the thermaloxide film 6 is etched from the surface of the silicon wafer 5. Afterthe silicon wafer 5 is washed or rinsed, the photo-resist layer isremoved by solvent, and the silicon wafer 5 is rinsed. In this way, asecond opening 9 is formed in the thermal oxide film 6. Subsequently, asshown in FIG. 6D, the exposed portion of the silicon wafer 5 isanisotropically etched by potassium hydroxide solution, so that aconcave portion 11 having (111) surface is formed. Then, as shown inFIG. 6E, the oxide film 6 remaining on the side on which the concaveportion 11 of the silicon wafer 5 is formed is perfectly etched bybuffered hydrofluoric acid.

[0083] Next, as shown in FIG. 6F, a copper film 12 is formed on thesurface of the side on which the concave portion of the silicon wafer 5is formed by a sputtering method to have the thickness of 1 μm.Subsequently, as shown in FIG. 6G, a photo-resist layer 13 is coated onthe copper film 12. The photo-resist layer 13 is exposed, developed andpatterned.

[0084] Next, an Au film 14 is formed on the copper film 12 by anelectrolytic plating method to have the thickness of 5 μm. Subsequently,as shown in FIG. 6H, the photo-resist layer 13 is removed by solvent.Then, the silicon wafer 5 is immersed in etching solution composed ofsulfuric acid of 5% and hydrogen peroxide water of 5 %. The copper film12 is etched by 0.8 μm. Through this step, the copper film 12 is madethin. Thus, it is possible to suppress stress at a time of removal ofthe mirror element 1 at a later process, resulting in reduction of adefect.

[0085] It should be noted that portions 14 (FIG. 7) extending in alateral direction of the Au film can be used as connection portions tothe optical circuit substrate 2. In this case, resin may be filled inthe space of the concave portion 11 after the formation of the Au film.Also, FIG. 7 is a plan view showing a die 5 for the mirror element 1formed as mentioned above. The optical axis of an incident light isshown by a dashed line. As shown in FIG. 7, the mirror element 1 formedin the concave portion 11 of the die 5 has connection portions 14 to theoptical circuit substrate 2 on both ends. The connection portions 14 aredisposed in a direction orthogonal to an incident direction of a lightbeam.

[0086] Next, the mirror element 1 is connected to the optical circuitsubstrate 2. As shown in FIG. 8A, connection pads 15 for the mirrorelement 1 are formed on the optical circuit substrate 2 by a goldplating method. Besides, a groove 16 for fixing an optical fiber andoptical element connection electrodes 17 are formed. The optical circuitsubstrate 2 and the silicon wafer 5 on which the Au films 14 are formedare adjusted in position by a connection unit (not shown). After that,the Au films 14 are connected to the optical circuit substrate 2 underthe condition of the temperature of 370° C. and the pressure of 1 N/cm²(100 g Weight/cm²). Then, the silicon wafer 5 is lifted up. At thistime, the copper film 12 is peeled from the silicon wafer die 5. Themirror element 1 remains on the optical circuit substrate 2 in a statein which the mirror element 1 is covered by the copper film 12. FIG. 8Bshows the mirror element 1 after the movement onto the optical circuitsubstrate 2. FIG. 9A is a plan view showing the mirror element 1 afterthe mount, and FIG. 5B is a front view showing the mirror element 1. Themirror element 1 has the shape that both upper ends of atriangular-prism shape in an axis direction a are cut away in a slantdirection.

[0087] The optical circuit substrate 2 on which the mirror element 1 isleft is immersed in etching solution composed of sulfuric acid of 5% andhydrogen peroxide water of 5%, so that the copper film 12 on the Au film14 is etched. Thus, the Au film 14 is exposed. Subsequently, an opticalfiber 3 and a photo-diode PD 4 are mounted on the optical circuitsubstrate 2, respectively. When a light beam is inputted to the opticalfiber 3, the light beam is reflected on the mirror element 1, andinputted to a light receiving section of the photo-diode PD 4. At thistime, loss caused by the reflection on the mirror element 1 isapproximately similar to a reflection rate of Au.

[0088] Especially, as shown in FIG. 10, when the optical fiber 3 isdisposed in a deep groove, there may be a case that an optical axis ofthe optical fiber 3 is located below the reflection surface of themirror element 1 mounted on the optical circuit substrate 2. In thiscase, however, a portion of the optical circuit substrate to which themirror element 1 should be connected is etched so that the reflectionsurface of the mirror element 1 can be coincident with the optical axisof the optical fiber. Thus, the light beam can be effectively reflectedby the mirror element 1. Also, the light beam is transmitted through airbetween the optical fiber 3 and the mirror element 1 and between themirror element 1 and the photo-diode PD 4. In this case, resin may befilled between the optical fiber 3 and the mirror element 1 and betweenthe mirror element 1 and the photo-diode PD 4. If a refractive index inan outer circumference of the optical fiber 3 is 1.45, it is desirablethat the resin has a refractive index between 1.34 and 1.56, namely, ina range of 1.45 ±0.11. This filling operation can suppress the losscaused by Fresnel reflection on air interface, resulting in reduction inthe optical coupling loss.

[0089] In the above-mentioned description, the copper film 12 functionsas a protective film of the reflection film (Au film) 14 and alsoenables the reflection film 14 to have a flat surface.

[0090]FIGS. 11A to 11H show a second fabricating method for the mirrorelement 1 used in the optical circuit according to the first embodimentof the present invention. The appearance of the mirror element 1 ispyramid-shaped, and the inside thereof is hollow. The mirror element 1is composed of three layers, and an outer layer is a rhodium film. Anickel film is formed on an inner side of the rhodium film. A gold filmis further formed on an inner side of the nickel film. The plane of aring-like rectangle that is the lower surface of the mirror element 1 iscomposed of the gold film. Platinum, palladium, gold, nickel,nickel-boron alloy and chrome are preferably used instead of rhodium.

[0091] At first, as shown in FIG. 11A, a silicon wafer die 5 is preparedwhich has the diameter of 6 inches and the thickness of 1 mm. Thesilicon wafer die 5 has the crystal orientation (100) plane. The thermaloxide films 6 are formed on both sides of the silicon wafer die 5. Thethickness of the thermal oxide film 6 is 1 μm. The photo-resist layer 7is coated on a first thermal oxide film. The thickness of thephoto-resist layer 7 is 5 μm. The photo-resist layer 7 is exposed by useof a mask. The silicon wafer die 5 is immersed in development solutionfor 10 minutes, and rinsed and patterned, so that an opening 8 is formedon the thermal oxide film 6, as shown in FIG. 11B.

[0092] The silicon wafer die 5 on which the opening 8 has been formed isimmersed in buffered hydrofluoric acid and rinsed to remove the portionof the first thermal oxide film 6 corresponding to the opening 8, asshown in FIG. 1C. After the removal, the photo-resist layer 7 is removedby solvent. Subsequently, the silicon wafer die 5 is washed to form theopening 9. Subsequently, as shown in FIG. 1D, the silicon wafer die 5 isanisotropically etched by use of potassium hydroxide solution of 10%,and a pyramid-shaped concave portion, namely, an etch pit 11 is formed.The pyramid-shaped concave portion 11 has a crystal orientation (100)plane as the concave portion surface. The pyramid-shaped concave portion11 is rectangular on the open side, as shown in FIG. 12. Thepyramid-shaped concave portion 11 is the space in a form of aquadrangular pyramid. The bottom side of the pyramid-shaped concaveportion 11, namely, the side of the opening is square-shaped. The lengthof one side is about 70 μm as shown in FIGS. 11 and 11E. As shown inFIG. 7E, the remaining portion of the first thermal oxide film 6 isremoved by buffered hydrofluoric acid.

[0093] Next, as shown in FIG. 11F, the copper film 12 is formed on theexposed surface of the silicon wafer die 5 and the pyramid-shapedconcave portion 11. The thickness of the copper film 12 is 1 μm. Aphoto-resist layer is formed on the copper film 12. The photo-resistlayer is exposed and developed by use of a preset mask. The patternedphoto-resist layer 13 is formed in this way. A portion of the copperfilm 12 formed in the pyramid-shaped concave portion 11 is not coveredby the photo-resist layer 13. The portion of the copper film 12 isexposed. An opening of the photo-resist layer 13 is rectangle-shaped. Asshown in FIG. 12, the longer side is 200 μm, and the shorter side is 60μm. A plating film 14 is formed on the surface of the quadrangularpyramid where the copper film 12 is exposed, by the electrolytic platingmethod. The plating film is the portion forming the mirror element 1,and is formed of three layers in the form of the quadrangular pyramid.An outer layer, namely, a bottom layer in FIG. 11G is made of a rhodiumfilm, a nickel film is formed on an inner side of the rhodium film, anda gold film is further formed on an inner side of the nickel film. Then,the gold film is exposed. The thickness of the rhodium film is 0.1 82 m,the thickness of the nickel film is 10 μm, and the thickness of the goldfilm is 1 μm.

[0094] Next, the photo-resist layer 13 is solved by organic solvent, andthe silicon wafer die 5 is immersed in the etching solution composed ofsulfuric acid of 5% and hydrogen peroxide of 5%, so that the copper film12 is etched by the thickness of 0.8 μm. In the thus-thinned copper film12, the stress when the copper film 12 is peeled is reduced at alater-described peeling step. As shown in FIGS. 12 and 11G, thecircumference of the pyramid-shaped concave portion 11 is concealed by aphoto-resist layer, and the plating film 14 is not formed on theconcealed portion. Thus, when the plating film 14 is peeled from thesilicon wafer die 5, the thinned copper film is easily bent by thestress because of the shapes. Hence, it is easy to carry out a peelingprocess.

[0095] Next, as shown in FIG. 11H, the photo-resist layer 13 and thecopper film 12 are removed to then complete the plating film 14 on thesilicon wafer die 5.

[0096]FIGS. 13A to 13D show a method for assembling the mirror element 1according to the first embodiment, which is fabricated by the secondfabricating method, on the optical circuit substrate 2. The plating film14 of the mirror element 1 is composed of a quadrangular-pyramid-shapedplating film portion 14A and rectangular plating films 14B integrallyextending on both sides of the quadrangular-pyramid-shaped plating filmportion 14A, as shown in FIG. 12.

[0097] A gold connection protrusion 18 is formed on the optical circuitsubstrate 2. In the gold connection protrusion 18, the horizontalsectional portion is square-shaped, and the one side is 60 μm. Theheight of the gold connection protrusion is 50 μm. The mirror element 1is positioned and disposed such that a bottom surface of an end portionof the plating film 14 meets a top surface of the gold connectionprotrusion 18. After that, the optical circuit substrate 2 is heated tothe temperature of 370° C. The silicon wafer die 5 having the mirrorelement 1 is pushed against the gold connection protrusion 18 in theforce of 1 N (about 100 g weight). The gold connection protrusion 18 andthe gold layer of the bottom layer of the mirror element 1 are connectedto each other by the pushing force through this heating operation. Afterthe completion of this connecting operation, the silicon wafer die 5 isremoved from the optical circuit substrate 2. Through this removal, themirror element 1 remains on the optical circuit substrate 2. At the timeof the removal, the mirror element 1 is connected to the gold connectionprotrusion 18. Thus, the mirror element 1 is easily removed from thesilicon wafer die 5. Since the stress is reduced as mentioned above, theremoval operation is easily carried out.

[0098] As mentioned above, the whole of the optical circuit substrate 2on which the mirror element 1 remains is immersed in etching solutioncomposed of sulfuric acid of 5% and hydrogen peroxide of 5%, so that thecopper film on the plating film 14 is removed. Through removal of thecopper film, the rhodium film is exposed as the surface of the platingfilm 14. The rhodium film effectively reflects the light.

[0099] As shown in FIG. 13A, gold pads 19 are further formed on twopositions on the optical circuit substrate 2. The gold pads 19 aredisposed on both sides of the optical axis of the optical guide device3. As shown in FIG. 13B, both sides of the rectangular plating portion14B are pushed against the optical circuit substrate 2, namely, in thelower direction. Thus, as shown in FIG. 13C, the mirror element ispushed down to the optical circuit substrate 2 by a coupling methodsimilar to a single point TAB (Tape Automated Bonding). In this way, themirror element 1 is fixed to the gold pads 19. Heat and supersonic maybe applied to the connection during this pushing operation, so that theconnection is heated to 400 ° C. At the time of this connectionoperation, the position of the mirror element 1 is adjusted in both theX and Y directions. The position of the quadrangular-pyramid-shapedplating film portion 14A is adjusted within an error range of 1 μm.

[0100] The quadrangular-pyramid-shaped plating film portion 14Aconnected to the optical circuit substrate 2 after the positionaladjustment as mentioned above is used as the mirror element 1, as shownin FIG. 5. The photo-diode 4 is positioned and mounted above the upperside of the quadrangular-pyramid-shaped plating film portion 14A.Electrodes of the photo-diode 4 are connected to wiring electrodes (notshown) on a waveguide circuit by solder. The width of the gap betweenthe end of the optical guide device 3 and thequadrangular-pyramid-shaped plating film portion 14A is 10 μm.

[0101] As shown in FIG. 13B, after the mirror element 1 is connected tothe optical circuit substrate 2, an electrolytic plating operation maybe further carried out to the surface of the plating film 14. Throughthis Au plating operation, the reflection rate of the mirror element 1can be made higher than that of the rhodium Rh, resulting in reductionof the coupling loss.

[0102]FIG. 14 shows the structure of the mirror element 1 fabricated bythe third fabricating method of the present invention. The mirrorelement 1 is moved from the silicon wafer die 5 to the optical circuitsubstrate 2, and connected through the gold film to the optical circuitsubstrate 2. The quadrangular-pyramid-shaped plating film portion 14A ofthe mirror element 1 differs from the mirror element 1 formed by thesecond fabricating method in that the material of the abovequadrangular-pyramid-shaped plating film portion 14 is changed. In themirror element 1 according to the second fabricating method, thereflection film is the rhodium film. However, in the mirror element 1according to the third fabricating method, photosensitive polyimide(PIMEL commercially available from Asahi Chemical Industry Co., Ltd.) isused for the reflection film.

[0103] In FIG. 11G, instead of the formation of the plating film 14, thephotosensitive polyimide is coated by use of a spin coat method, and isexposed and developed. Thus, a photosensitive polyimide film ispatterned to form the mirror element. Then, the mirror element 1 isconnected to the optical circuit substrate 2, similarly to theabove-mentioned examples. Thereafter, the silicon wafer die 5 havingsuch a photosensitive polyimide film is heated at the temperature of350° C. for two hours. The photosensitive polyimide film starts reactionat 350° C., and the volume is reduced or contracted by about 40% inconjunction with the reaction. At a time of such contraction, the topsurface of the mirror element 1 in the state shown in FIG. 11H isdepressed because of the contraction. At the same time, the platingsurface is pulled by residual stress that cannot be relaxed through thedepression of the top surface. The copper film is peeled from thesilicon wafer die 5 due to this residual stress. The photosensitivepolyimide film is not almost deformed in ridgeline portions of thequadrangular pyramid. However, the center of each reflection surface 23is depressed as shown by hatching 22 in FIG. 15. Such a concave portionforms a concave surface 24 of the mirror element 1. The silicon waferdie 5 is removed from the optical circuit substrate 2, and the mirrorelement 1 is left on the optical circuit substrate 2. Thus, the mirrorelement 1 is connected to the optical circuit substrate 2. The processof removal and connection of the mirror element 1 to the optical circuitsubstrate 2 is as described above.

[0104] The mirror element 1 on which such a concave surface 24 is formedfunctions as a concave mirror, as shown in FIG. 16. Light which isoutputted from the optical guide device 3 spreads to the angle of about20 degrees. Thus, the light spreads to the diameter of 32 μm φ in theoptical path length of 60 μm. The light is converged by the concavesurface 24, and inputted to the photo-diode 4 as a substantiallyparallel beam. The curvature radius of the concave surface is 160 μm.The light beam inputted to the photo-diode 4 is reduced from 32 μm φ to28 μm φ. The mirror element according to the third fabricating methodcan effectively send the light beam to the device, as compared with themirror elements according to the first and second fabricating methods.

[0105] When the above-mentioned polyimide is used as the resin, theresin is never deformed at later steps such as a solder re-flow (heattreatment at 230 ° C.), and a rinsing operation (contact with organicsolvent). Thus, the shape of the mirror element can be kept in theoriginal state at the time of the formation.

[0106]FIGS. 17 and 18 show the sections of the mirror element andconcave portion 11 of a die fabricated by a fourth fabricating method.Similarly to the mirror element according to the first fabricatingmethod, the silicon etch pit 11 is fabricated, the copper film 12 isformed, and the photo-resist layer 13 is coated and patterned. In anopening 11, only the concave portion of the die is opened as shown inFIG. 17. The electrolytic plating operation is carried out and thephoto-resist layer 13 for forming the opening 11 is removed. As shown inFIG. 18, resin having an adhesive property and a photosensitive propertyis coated to fill a concave portion formed by the plating film 14. Then,the resin film is patterned through the exposure and the developmentsuch that resin 22 remains only in the portion of the plating film 14.As the resin, resin composition may be used which contains an activeenergy line reaction resin and an active energy line polymerizationinitiator.

[0107] As the active energy line reaction resin, the material issuitable which is hardened by a radiation of an active energy line suchas an ultraviolet ray, an electronic line, an X-line, and the hardenedsubstance provides an adhesion hardening property through heatingtreatment. Specifically, phenol novolak type epoxy resin, cresol/volaktype epoxy resin, glycylamine type epoxy resin and biphenyl type epoxyresin are preferable which provide the hardening property resulting fromthe radiation of the active energy line. Especially, the substance ispreferably used in which unsaturated-base acid such as acrylic acid,methacrylic acid, crotonic acid, maleic acid, maleic acid monomethyl,maleic acid monopropyl, maleic acid monobutyl, and sorbic acid is madeto react with epoxy resin having fluorene skeleton and the reactionresult is made into ester. The active energy line polymerizationinitiator generates radicals by radiating an active energy line, and canpromote the polymerization of the active energy line reaction resin onthe basis of the physical property of the initiator such as a hydrogendraw reaction and a radical cleavage reaction. The representativesubstance of the hydrogen draw type is a benzophenone class. Abenzildi-methylkethal class is exemplified as the radical cleavage type.Moreover, a compound of a thio-xanthone system may be used. One kind ortwo kinds or more of those materials can be mixed with the active energyline reaction resin.

[0108] As shown in FIGS. 19A and 19B, the mirror element 1 is connectedto the optical circuit substrate 2. As shown in FIG. 19A, positioningmarks 25 used to mount the mirror element 1 are provided on the opticalcircuit substrate 2. At the step shown in FIG. 19B, the silicon waferdie 5 in which the mirror element is formed is positioned and disposedon the optical circuit substrate 2 by a connection unit (not shown).After that, the optical circuit substrate 2 is heated, and the mirrorelement 1 is connected to the optical circuit substrate 2 by the resin22. Then, the silicon wafer die 5 is removed from the substrate 2. Inthis way, the mirror element 1 is left on the optical circuit substrate2. The resin fills in the mirror element 1 to increase the strength ofthe mirror element 1 and improve the reliability. Also, it is notnecessary to provide the connection portions 14B with the opticalcircuit substrate 2. Therefore, the space saving can be attained,resulting in reduction of the restriction on an electric surface wiringand the like.

[0109]FIGS. 20 and 21 show an optical circuit according to the thirdembodiment of the present invention. The mirror element 1, apiezoelectric element 28, the optical fiber 3 and an optical element 4are mounted on the optical circuit substrate 2. The structure of acantilever is employed in the vicinity of a mount portion 31 of themirror element 1 as shown in FIG. 21. In short, the vicinity of themount portion 31 has the structure in which one connection portion isleft and the thickness of the mount portion 31 is thin. Thepiezoelectric element 28 is connected to a back surface of the mountportion of the mirror element 1. The piezoelectric element 28 iscomposed of zirconic acid lead titanate system material and goldelectrodes formed on both main surfaces in the thickness direction. Thepiezoelectric element 28 operates to expand and contract in response toapplication of a voltage, so that the mirror element 1 mounted on themount portion 31 of the cantilever is moved in the height direction.Thus, it is possible to change an optical coupling efficiency betweenthe optical fiber 3 and the optical element 4. If the piezoelectricelement 28 is expanded and contracted so that the optical couplingefficiency can be changed between the maximum (on) and the minimum(off), this assembly can be used as a switch.

[0110] The optical circuit having the structure shown in FIGS. 20 and 21is fabricated as follows. Silicon is used for the optical circuitsubstrate 2. At first, an anisotropic etching process is carried out tothe optical circuit substrate 2 to form a mount groove for mounting theoptical fiber 3. Next, a dry etching is carried out to front and backsurfaces of the optical circuit substrate 2 to form the structure of thecantilever. The length of the cantilever is 5 mm, and the thicknessthereof is 50 μm. Here, the surface on which the optical element 4 andthe mirror element 1 are mounted is referred to as a front surface, anda surface opposite to the front surface is referred to as a backsurface.

[0111] Next, the mirror element is formed by the first fabricatingmethod. Subsequently, after a jig is installed below the cantilever, themirror element 1 is mounted on the optical circuit substrate 2 by a goldpress fitting process. Then, the photo-diode PD 4 is mounted on thesubstrate 2 by solder. Then, a piezoelectric element 28 having thethickness of 50 μm is fixed by adhesive to the back surface of thecantilever of the silicon substrate 2. By this structure, the mirrorelement 1 can be moved in a height direction by about 20 μm.

[0112] After all the parts were mounted, a light beam was inputted tothe optical fiber 3, and then a light reception efficiency of thephoto-diode PD 4 was measured. At this time, the light receptionefficiency was 70%. Then, a voltage was applied to the piezoelectricelement 28 to move the mirror element 1 in the height direction suchthat a light amount received by the photo-diode PD is in the maximum. Atthis time, the light coupling efficiency was 95%, and it was possible tosubstantially maximize the efficiency.

[0113] In this embodiment, the piezoelectric element is used to drivethe mirror element. However, instead of the piezoelectric element, anelectric distortion actuator, a magnetic distortion actuator, a phasetransition material and the like may be used. Also, the adhesive is usedto connect the mirror element 1 and the optical circuit substrate 2.However, the piezoelectric material may be directly formed on thesubstrate 2.

[0114] Also, FIG. 22 shows an optical circuit according to a fourthembodiment of the present invention. Referring to FIG. 22, an assemblingstructure having two cantilevers may be employed in which piezoelectricelements 28 are adhered to respective back surfaces of the cantilevers.In this case, it is possible to change an angle between a reflectionsurface of the mirror element 1 and an optical axis. When the length ofthe cantilever is 3 mm and the piezoelectric elements 28 are driven suchthat one piezoelectric element is expanded and the other is contracted,the angle between the mirror element 1 and the optical axis can bechanged by about 20 degrees.

[0115] Referring to FIGS. 23A and 23B, a surface light emission typelaser is used as the optical element. The assembling structure can beused as a switch by driving the piezoelectric elements and controllinginput of an output light from the surface light emission type laser tothe optical fiber 3.

[0116] An actual example will be described below.

[0117] An etch pit is formed in the silicon wafer die 5. A copper filmis formed by sputtering and photolithography. A rhodium film is formedto have the film thickness of 0.5 μm by an electrolytic plating method.This electrolytic plating film is formed to have a strong tensilestress. For this tensile stress, the sputtered film is peeled from thesilicon wafer die 5 during the plating operation. As a result, asectional shape shown in FIG. 24 can be obtained as the mirror element.In ridgeline portions having such shape, deformation is never inducedfor the geometric condition, even in the application of the stress. Theapplication of the tensile stress from the ridgeline causes thereflection surface of the mirror element to receive the deformationstress. Although the tensile stress within the plane acts to protectthis deformation, the sum of those forces result in the peeling of thesputtering film, and also result in the deformation of the plating film.After that, a nickel plating film is formed to have the film thicknessof 5 μm, and a gold plating film is formed to have the film thickness of1 μm. After that, as mentioned above, the mirror element is connected tothe optical circuit substrate 2. In the thus-formed mirror element 1,the reflection surface is a concave portion, and the curvature radius is70 μm. In this way, the light beam emitted from the optical guide devicecan be inputted to the photo-diode to have the diameter of 5 μm φ.

[0118] As the resist layer 13 shown in FIG. 6G, a resist layer 13′ maybe used which is distorted as shown in FIG. 25. The resist layer 13′ isrectangular, and formed in a form of ring. One side of the hole is 100μm, and the other side is 70 μm. When such a resist layer 13′ is used toetch the silicon wafer, a trapezoid protrusion having a concave portion26 in a center is formed as shown in FIG. 26. The mirror element isformed in such a trapezoid concave portion. The formed mirror element 1has a prism shape as shown in FIG. 27. The mirror element 1 is connectedto the optical circuit substrate 2. In this connecting operation, thegold connection protrusion 18 shown in FIG. 13 is unnecessary. Themirror element 1 is connected to a gold electrode 41 located 30 μm froman end portion of the optical guide device 3. In this case, there-bonding operation is unnecessary. Thus, the number of steps can bereduced.

[0119] A (3, 3, 25) plane is employed as a plane orientation of siliconto be etched. As mentioned above, the etch pit is formed until theappearance of the (111) plane. An angle between the surface of the etchpit and the surface of the silicon is 45 degrees. The rhodium film isformed in the silicon wafer die 5 by the electrolytic plating method sothat the rhodium film has the film thickness of 0.5 μm. The mirrorelement 1 formed thus is connected to the optical circuit substrate 2,as mentioned above, as shown in FIG. 28. In FIG. 28, a surface lightemission diode 4 is mounted instead of the photo-diode 4. The reflectionsurface of the mirror element 1 has the angle of 45 degrees with respectto the end surface of the optical guide device 3. The light beam emittedfrom the surface light emission diode 4 is reflected on the concaveportion of the mirror element, and converged and inputted to the opticalguide device 3. The concave portion of the mirror element is gentlycurved from the center of the reflection surface of the mirror elementto the end. The curvature radius of the curved portion to which thelight beam is emitted is 70 μm.

[0120]FIGS. 29A to 29E show an optical circuit according to the fifthembodiment of the present invention. The method shown in FIGS. 6A to 6His used in the original state, as the process for fabricating the mirrorelement 1 shown in FIG. 29A to form the silicon etch pit. However, atthe step of FIG. 11G, a Ni layer is formed on the copper film 12 by theelectrolytic plating method so that the Ni layer has the film thicknessof 5 μm. Then, a Pb/Sn layer is formed on the Ni layer so that the Pb/Snlayer has the film thickness of 5 μm. After the formation of such aplating film 14 in a form of lamination, the photoresist layer 13 isremoved by the solvent, as shown in FIG. 6H. Next, the silicon wafer die5 is immersed in etching solution composed of sulfuric acid of 5% andhydrogen peroxide of 5%. The copper film 12 is removed by 0.8 μm throughthe etching process. Through the formation of such a laminated platinglayer, the stress is further decreased when the mirror element is peeledfrom the silicon wafer die 5. Thus, it is possible to further decreasean error occurrence possibility.

[0121] The silicon wafer 5 on which the mirror element 1 is formed asmentioned above and the optical circuit substrate 2 on which the opticalguide device 3 is formed are positioned by a connection device (notshown). Then, Pb/Sn solder is used to connect the mirror element 1 tothe optical circuit substrate 2 on a predetermined position at thetemperature of 230° C. Next, the mirror element 1 is peeled from thesilicon wafer die 5, and mounted on the optical circuit substrate 2, asshown in FIG. 29A. It should be noted that the mirror element 1 isquadrangular-pyramid-shaped.

[0122] Next, as shown in FIG. 29B, a resist layer 32B is coated on theoptical circuit substrate 2 from the top side. Then, as shown in FIG.29D, a chrome/gold layer 33 is formed by a sputtering method. Instead ofgold, a sample in which a film composed of one of aluminum, silver,copper, platinum, titanium and nickel is formed is also fabricated. Inorder to protect the metal layer as the reflection surface, agermanium/silicon oxide film is formed on the reflection surface.Subsequently, the resist layer 32 is removed as shown in FIG. 29E.

[0123] The photo-diode PD 4 was mounted on the substrate 2 of eachsample. It was confirmed that when the light beam was inputted to theoptical waveguide, the light beam was reflected on the mirror element 1,and the light was inputted to the light receiving section of thephoto-diode PD 4. It was also confirmed that the loss caused by thereflection on the mirror element 1 was substantially similar to thereflection rate of the metal used in the reflection surface.

[0124] In the above-mentioned examples, after the mirror element 1 ismounted on the substrate, the reflection surface of the mirror elementcan be formed by use of the metal suitable for the reflection such asgold, without using a wet process. In many cases, the optical circuitsubstrate uses the optical waveguide in which the optical loss isincreased because of absorption of water. However, through theabove-mentioned process, the mirror can be mounted on the substratewithout any contact between the optical waveguide and the water. Also,by the usage of the solder, the mirror can be mounted on the substrateto have a low heat resistance. The solder material is not limited to thePb/Sn. As shown in FIG. 29C, by using a metal mask 34 instead of theresist layer 32, and by forming an opening 35 in a portion of the metalmask 34 corresponding to the mirror element, the reflection metal filmmay be formed.

[0125] The same process as that of the first embodiment, namely, thesteps of FIGS. 6A to 6F are used, as they are to fabricate the siliconetch pit. After the step of FIG. 6F, an Au layer having the thickness of5 μm is formed on the copper film 12 by use of the electrolytic platingprocess. Moreover, a Ni layer having the thickness of 5 μm is formed onthe Au layer. Then, the Au layer having the thickness of 5 μm is formedon the Ni layer. In such a layer structure, there was a case that thelamination plating film is thinly formed near vertex portionscorresponding to the concave portion of the silicon wafer die. In thiscase, when the plating lamination is connected to the substrate and themirror element is peeled from the silicon wafer, vertex portions of amirror element 1′ are damaged as shown in FIG. 30A. In order to copewith such a problem, in addition to use of a Ni−P layer, the laminationfilm structure is changed to 1 μm Au/0.2 μm (Ni—p)/5 μm Ni/0.2 μmP/5 μmAu. Accordingly, the film formation property becomes uniform in theentire concave portion. In this case, the mirror element 1 can bemounted on the substrate without any damage to the vertex portions ofthe mirror element 1, as shown in FIG. 30B.

[0126] Similarly to the above case, the silicon etch pit is fabricated.After the step of FIG. 6F, an Au layer is formed on the copper film 12to have the film thickness of 5 μm by use of the electrolytic platingprocess. Next, when the mirror element is connected to the substrateusing the solder of Au/Sn, the solder and Au are diffused to form analloy 36 on the reflection surface as shown in FIG. 31A. A measuredreflectance was 80%, which is decreased to a value less than thereflectance of Au. In order to cope with such decrease, the laminationstructure is changed to 5-μm Au/5-μm Pt/1-μm Au. Similarly to the abovecase, the solder is used to connect the mirror element to the substrate.At this time, as shown in FIG. 31B, alloy was not formed on thereflection film, and the reflection surface is formed of only Au. Ameasured reflectance was 98%. This reason would be that the Pt middlefilm prevents that the connection solder is diffused up to Au in thereflection film.

[0127] As the result of the fabrication of such a mirror element, anindividual prism and lens are not required which are conventionallynecessary. Also, the mirror element can be mounted on any substrate.

[0128] As mentioned above, the various embodiments and modifications andthe various fabricating methods have been described. However, thoseskilled in the art could understand that they can be mixed and attainedin the range of no contradiction.

[0129] The optical circuit according to the present invention and themethod for fabricating the same can make it possible to fabricate theoptical path conversion element at a low cost. The die whose treatmentis easy is used, and the mirror element is easily fabricated by use ofthe die. Such a mirror element can be easily connected to any opticalcircuit substrate. Moreover, the curvature of the reflection surface ofthe mirror can be easily formed at the same step.

What is claimed is:
 1. A method for fabricating an optical circuit, comprising the steps of: (a) connecting a mirror element with a protection film formed within a die of a semiconductor, to a substrate at a predetermined position; (b) peeling from said semiconductor die, said mirror element with said protection film connected to said substrate; and (c) removing said protection film such that a reflection surface of a reflection film of said mirror element is exposed.
 2. The method according to claim 1, wherein said mirror element with said protection film is installed in a tip portion of at least one cantilever of said substrate, and said method further comprises the step of: mounting an expending and contracting member for moving said tip portion upwardly and downwardly below said mirror element or on a back surface of said tip portion.
 3. The method according to claim 1, wherein said expending and contracting member is one of a piezoelectric element, an electric distortion actuator, a magnetic distortion actuator, and a phase transition material.
 4. The method according to claim 1, wherein said (b) peeling step comprises the step of: thinning a thickness of said protection film in a peripheral portion of said mirror element.
 5. The method according to claim 1, wherein said (c) removing step comprises the step of: removing said protection film by a wet etching.
 6. The method according to claim 1, wherein said (a) connecting step comprises the steps of: (d) forming said protection film to cover an inner surface of a concave portion corresponding to said semiconductor die; and (e) forming a reflection film of said mirror element to at least cover said protection film in said concave portion.
 7. The method according to claim 6, wherein said (e) forming step comprises the step of: forming said reflection film by an electrolytic plating process.
 8. The method according to claim 6, wherein said reflection film is one of a gold film, a lamination film of rhodium film-nickel film-gold film, a lamination film of platinum film-nickel film-gold film, a lamination film of palladium film-nickel film-gold film, a lamination film of gold film-nickel film-gold film, a lamination film of nickel film-boron alloy film-nickel film-gold film, a lamination film of nickel film-gold film, a lamination film of chrome film-nickel film gold film, a photosensitive polyimide film, a lamination film of gold film-(Ni—P) film/Ni film-P film-Au film, and a lamination film of Au film-Pt film-Au film.
 9. The method according to claim 6, further comprising the step of: (f) filling a remaining concave portion after the formation of said reflection film with predetermined material.
 10. The method according to claim 9, wherein said predetermined material is a resin composition containing an active energy line polymerization initiator and an active energy line reaction resin.
 11. The method according to claim 1, wherein said mirror element has connection auxiliary films in a direction of said reflection surface, and said (a) connecting step comprises the steps of: connecting said connection auxiliary films to said substrate; and connecting said mirror element to said predetermined position of said substrate after said (b) peeling step.
 12. The method according to claim 1, wherein said reflection surface of said mirror element has a flat surface.
 13. The method according to claim 1, wherein said reflection surface of said mirror element has a concave surface.
 14. A method for fabricating an optical circuit comprising the steps of: (a) connecting a mirror element with a protection film formed within a die of a semiconductor to a substrate at a predetermined position; (b) peeling from said semiconductor die, said mirror element with said protection film connected to said substrate; and (c) forming a reflection film of said mirror element on said protection film.
 15. The method according to claim 14, wherein said mirror element with said protection film is mounted to a tip portion of at least one cantilever of said substrate, and said method further comprises the step of: mounting an expending and contracting member for moving said tip upwardly and downwardly below said mirror element or on a back surface of said tip portion.
 16. The method according to claim 14, wherein said expending and contracting member is one of a piezoelectric element, an electric distortion actuator, a magnetic distortion actuator, and a phase transition material.
 17. The method according to claim 14, wherein said (b) peeling step comprises the step of: thinning a thickness of said protection film in a peripheral portion of said mirror element.
 18. The method according to claim 14, wherein said (a) connecting step comprises the steps of: (d) forming said protection film to cover an inner surface of a concave portion corresponding to said semiconductor die; and (e) forming said mirror element to at least cover said protection film in said concave portion.
 19. The method according to claim 18, wherein said (e) forming step comprises the step of: filling a remaining concave portion after the formation of said mirror element with predetermined material.
 20. The method according to claim 19, wherein said predetermined material is a resin composition containing an active energy line polymerization initiator and an active energy line reaction resin.
 21. The method according to claim 14, wherein a reflection surface of said mirror element has a flat surface.
 22. The method according to claim 14, wherein said reflection surface of said mirror element has a concave surface.
 23. A method for fabricating a mirror element comprising the steps of: (a) forming a protection film to cover an inner surface of a die formed in a semiconductor substrate; (b) forming a mirror element film to at least cover said protection film in said inner surface of said die; and (c) peeling from said semiconductor substrate said mirror element film together with said protection film.
 24. The method according to claim 23, further comprising the step of: (d) removing said protection film from said mirror element such that said mirror element film functions as a reflection film.
 25. The method according to claim 23, further comprising the step of: (e) forming a reflection film on said protection film formed on said mirror element film.
 26. The method according to claim 25, wherein said reflection film is one of a lamination film of chrome film-gold film, a lamination film of chrome film-aluminum film, a lamination film of chrome film-silver film, a lamination film of chrome film-copper film, a lamination film of chrome film-palladium film, a lamination film of chrome film-titanium film, and a lamination film of chrome film-nickel film.
 27. The method according to claim 24, wherein said (a) forming step comprises the steps of: (f) forming said protection film to cover said inner surface of said die formed in said semiconductor; and (g) forming said mirror element film to at least cover said protection film in said inner surface of said die.
 28. The method according to claim 27, wherein said (g) forming step comprises the step of: forming said mirror element film by an electrolytic plating process.
 29. The method according to claim 27, wherein said mirror element film is one of a gold film, a lamination film of rhodium film-nickel film-gold film, a lamination film of platinum film-nickel-film gold film, a lamination film of palladium film nickel film-gold film, a lamination film of gold film-nickel film-gold film, a lamination film of nickel film-boron alloy film-nickel film-gold film, a lamination film of nickel film-gold film, a lamination film of chrome film-nickel film-gold film, a photosensitive polyimide film, a lamination film of gold film-(Ni—P) film/Ni film-P film-Au film, and a lamination film of Au film-Pt film-Au film.
 30. The method according to claim 27, further comprising the step of: (h) filling a remaining concave portion after the formation of said mirror element film with predetermined material.
 31. The method according to claim 30, wherein said predetermined material is one of a resin composition containing an active energy line polymerization initiator and an active energy line reaction resin.
 32. The method according to claim 31, wherein said active energy line reaction resin is one of phenol novolak type epoxy resin, cresol/volak type epoxy resin, glycylamine type epoxy resin and biphenyl type epoxy resin.
 33. The method according to claim 31, wherein said active energy line reaction resin is substance obtained by reacting unsaturated-base-acid such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic acid monomethyl, maleic acid monopropyl, maleic acid monobutyl, sorbic acid with epoxy resin having fluorene skeleton or epoxy resin portion of bromide of epoxy resin having fluorene skeleton, and by making into ester.
 34. The method according to claim 31, wherein said active energy line polymerization initiator is one kind or two kinds or more of a benzophenone class, a benzildi-methylkethal class and a compound of a thio-xanthone system.
 35. The method according to claim 23, wherein said (a) forming step further comprises the step of: etching a silicon substrate to form a concave portion corresponding to said die.
 36. The method according to claim 35, wherein an inner surface of said concave portion has one of a (100) surface and a (111) surface.
 37. The method according to claim 35, wherein said concave portion is one of a pyramid shape and a triangular pole shape in which both ends are cut down.
 38. The method according to claim 23, wherein said (c) peeling step comprises the step of: thinning said protection film in a peripheral portion corresponding to said mirror element film.
 39. The method according to claim 32, wherein said (c) stripping step comprises the step of: peeling said mirror element film from said die of said semiconductor after said mirror element film is connected to the substrate.
 40. The method according to claim 39, wherein said mirror element film has connection film portions used to connect to said substrate in a direction orthogonal to an optical axis at a time of a usage. 